In my efforts to study for the BIG immigration exam in March 2010, I am grateful for the P visa. Not only does the P visa follow the O visa alphabetically, but also the requirements for obtaining a P visa seem to logically follow the requirements for obtaining an O visa. Easy to remember.
An O visa requires extraordinary ability of a specific person, such as a perfomer, artist or athlete. The P-1 visa, on the other hand, is for a member of an entertainment group which has existed for at least one year; the group must have international recognition, not the individual performer. In fact, where the entertainer is coming to the U.S. under a reciprocal exchange program (P-2) or for a culturally unique program (P-3), the "international recognition" requirement is waived completely.
P visas are also available to athletes, whether professional or amateur, performing individually or as part of a group or team. Again, the standard is lower than for the O visa. Either the athlete is internationally recognized -- meaning recognized in at least 2 foreign countries -- or the event where she will be competing/performing is internationally recognized.